An urgent need exists in many fields for a method that is capable of selectively controlling the activation of various molecular agents. The desired improvements in activation include enhancements in spatial or temporal control over the location and depth of activation, reduction in undesirable activation of other co-located or proximal molecular agents or structures, and increased preference in the activation of desirable molecular agents over that of undesirable molecular agents. Various linear and non-linear photo-chemical and photo-physical methods have been developed to provide some such improvements for some such agents. However, in general the performance and applicability of these methods have been less than desired. Specifically, improved photo-activation methods are needed that may be used to selectively photo-activate a variety of molecular therapeutic agents while providing improved performance in the control of application of this photo-activation.
Application of optical radiation for probing or transformation of molecular agents has been known for many years. Linear optical excitation has been extensively studied as a means for achieving semi-selective activation of molecular therapeutic agents. For example, Tessman et al. (J. W. Tessman, S. T. Isaacs and J. E. Hearst, "Photochemistry of the Furan-Side 8-Methoxypsoralen-Thymidine Monoadduct Inside the DNA Helix. Conversion to Diadduct and to Pyrone-Side Monoadduct," Biochemistry, 24 (1985) 1669-1676) teach of the application of light at specific energies as a means for achieving partial selectivity in the formation of molecular bonds between target molecular agents and DNA (deoxyribonucleic acid). Kennedy et al. (J. C. Kennedy, R. H. Pottier and D. C. Ross, "Photodynamic Therapy with Endogenous Protoporphyrin IX: Basic Principles and Present Clinical Experience," Journal of Photochemistry and Photobiology, B: Biology, 6 (1990) 143-148) review progress on development and application of various photosensitive molecular agents for clinical treatment of disease. And Teuchner et al. (K. Teuchner, A Pfarrherr, H. Stiel, W. Freyer and D. Leupold, "Spectroscopic Properties of Potential Sensitizers for New Photodynamic Therapy Start Mechanisms via Two-Step Excited Electronic States," Photochemistry and Photobiology, 57 (1993) 465-471) teach of the use of spectroscopic properties for selection of candidate photo-active agents. Yet performance of these agents and specifically the methods used for their activation have not been as successful as desired. For example, Young (A. R Young, "Photocarcinogenicity of Psoralens Used in PUVA Treatment: Present Status in Mouse and Man," Journal of Photochemistry and Photobiology, B: Biology, 6 (1990) 237-247) presents strong evidence that the optical radiation used in common treatment regimes based on linear optical excitation of photosensitive molecular agents can itself produce disease and other undesirable side effects. Furthermore, a less than desirable penetration depth has plagued most efforts at linear optical excitation of molecular therapeutic agents, primarily as a consequence of the effects of optical scatter and of absorbency of the incident probe radiation at wavelengths near the linear absorption bands of these agents. In fact, virtually all examples of the use of linear optical excitation for molecular transformation are plagued by fundamental performance limits that are attributable to undesirable absorption and scatter of the incident optical radiation by the surrounding matrix, poor specificity in excitation of probe molecular species, and a lack of suitable physical mechanisms for precise control of the extent and depth of activation.
Various non-linear optical excitation methods have been employed in an effort to achieve specific improvements in the selectivity of photo-activation for certain applications, and to address many of the limitations posed by linear excitation methods. Excitation sources ranging from single-mode, continuous wave (CW) lasers to pulsed Q-switched lasers having peak powers in excess of 1 GW have been employed with these methods. For example, Wirth and Little (M. J. Wirth and F. E. Lytle, "Two-Photon Excited Molecular Fluorescence in Optically Dense Media," Analytical Chemistry, 49 (1977) 2054-2057) teach use of non-linear optical excitation as a means for stimulating target molecules present in optically dense media; this method is shown to be useful in limiting undesirable direct interaction of the probe radiation with the media itself, and provides a means for effectively exciting target molecular agents present in strongly absorbing or scattering matrices. Yeung et al. teach further use of non-linear optical excitation for highly specific excitation of target molecules present in very small volumes (M. J. Sepaniak and E. S. Yeung, "Laser Two-Photon Excited Fluorescence Detection for High Pressure Liquid Chromatography," Analytical Chemistry, 49 (1977) 1554-1556; M. J. Sepaniak and E. S. Yeung, "High-Performance Liquid Chromatographic Studies of Coal Liquids by Laser-Based Detectors," Journal of Chromatography, 211 (1981), 95-102; and W. D. Pfeffer and E. S. Yeung, "Laser Two-Photon Excited Fluorescence Detector for Microbore Liquid Chromatography," Analytical Chemistry, 58 (1986) 2103-2105). These works teach of the attractive performance advantages of non-linear optical excitation of target molecular agents present in complex matrices, specifically where reduced background excitation, low probe volumes, and complementary selection rules provided by non-linear methods aid in increasing selectivity of the analysis. Improved spatial control over the active region has been further developed by Wirth (M. J. Wirth and H. O. Fatunmbi, "Very High Detectability in Two-Photon Spectroscopy," Analytical Chemistry, 62 (1990) 973-976); specifically, Wirth teaches a method for achieving extremely high spatial selectivity in the excitation of target molecular agents using a microscopic imaging system. Similar control has been further applied by Denk et al. (W. Denk, J. P. Strickler and W. W. Webb, "Two-Photon Laser Microscopy," U.S. Pat. No. 5,034,613) who teach of a special confocal laser scanning microscope utilizing non-linear laser excitation to achieve intrinsically high three-dimensional control in the photo-activation of various molecular fluorophor agents on a cellular or sub-cellular scale. This microscope is used to excite molecular fluorophor agents added to biological specimens, which constitute an optically dense medium; the special properties of non-linear optical excitation are utilized to substantially limit excitation to a confocal region occurring at the focus of an objective lens, thereby allowing the possibility of three-dimensional imaging by sharply controlling the depth of focus. Control of photo-excitation for generation of luminescence-based images at the cellular and sub-cellular level is shown in target samples mounted on a stage. This microscope is also used for localized photolytic release of caged effect or molecules present in individual cells mounted on a stage, and is claimed to be useful for inducing additional photochemical reactions in such cells. However, reduction in photo-induced necrosis of cells located at the focal plane is claimed to be the primary benefit of this microscopy approach, based on the replacement of ultraviolet excitation radiation with near infrared radiation.
While the substantial body of prior art exemplified by these cited examples clearly demonstrates many attractive features of photo-activation methods, a general method for achieving selective photo-activation of one or more molecular agents with a high degree of spatial control that is capable of meeting the diverse needs of industry has not been previously taught Specifically, practical methods for effecting such control on scales that are significant for therapeutic uses or for general materials processing applications have not been previously taught.
Therefore, it is an object of the present invention to provide a method for the treatment of plant or animal tissue with a high degree of spatial selectivity.
It is further object of the present invention to provide such a method using a light source and photo-active materials to enhance the high degree of spatial selectivity.
It is another object of the present invention to provide such a method using wavelengths of light which are less harmful to the plant or animal tissue than the wavelengths of light currently used for the treatment of plant or animal tissue.
It is yet another object of the present invention to provide such a method using light which is less prone to scatter in and absorption by plant or animal tissue than the wavelengths of light currently used for the treatment of plant or animal tissue.
Consideration of the specification, including the several figures and examples to follow, will enable one skilled in the art to determine additional objects and advantages of the invention.